The following ICE's in beta and nightly: ```Rust struct Bug { a: [(); (|| { 0 })()] } ``` <details> <summary>Backtrace:</summary> ``` Compiling playground v0.0.1 (/playground) error[E0015]: calls in constants are limited to constant functions, tuple structs and tuple variants --> src/lib.rs:2:13 | 2 | a: [(); (|| { 0 })()] | ^^^^^^^^^^^^ error: internal compiler error: src/librustc_typeck/collect.rs:1969: to get the signature of a closure, use `closure_sig()` not `fn_sig()` thread 'rustc' panicked at 'Box<Any>', src/librustc_errors/lib.rs:882:9 stack backtrace: 0: backtrace::backtrace::libunwind::trace at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.40/src/backtrace/libunwind.rs:88 1: backtrace::backtrace::trace_unsynchronized at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.40/src/backtrace/mod.rs:66 2: std::sys_common::backtrace::_print_fmt at src/libstd/sys_common/backtrace.rs:77 3: <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt at src/libstd/sys_common/backtrace.rs:59 4: core::fmt::write at src/libcore/fmt/mod.rs:1052 5: std::io::Write::write_fmt at src/libstd/io/mod.rs:1426 6: std::sys_common::backtrace::_print at src/libstd/sys_common/backtrace.rs:62 7: std::sys_common::backtrace::print at src/libstd/sys_common/backtrace.rs:49 8: std::panicking::default_hook::{{closure}} at src/libstd/panicking.rs:204 9: std::panicking::default_hook at src/libstd/panicking.rs:224 10: rustc_driver::report_ice 11: std::panicking::rust_panic_with_hook at src/libstd/panicking.rs:476 12: std::panicking::begin_panic 13: rustc_errors::HandlerInner::bug 14: rustc_errors::Handler::bug 15: rustc::util::bug::opt_span_bug_fmt::{{closure}} 16: rustc::ty::context::tls::with_opt::{{closure}} 17: rustc::ty::context::tls::with_opt 18: rustc::util::bug::opt_span_bug_fmt 19: rustc::util::bug::bug_fmt 20: rustc_typeck::collect::fn_sig 21: rustc::ty::query::__query_compute::fn_sig 22: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query 23: rustc_mir::const_eval::fn_queries::provide::is_const_fn_raw 24: rustc::ty::query::__query_compute::is_const_fn_raw 25: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query 26: <rustc_mir::const_eval::machine::CompileTimeInterpreter as rustc_mir::interpret::machine::Machine>::find_mir_or_eval_fn 27: rustc_mir::interpret::terminator::<impl rustc_mir::interpret::eval_context::InterpCx<M>>::eval_fn_call 28: rustc_mir::interpret::step::<impl rustc_mir::interpret::eval_context::InterpCx<M>>::step 29: rustc_mir::const_eval::eval_queries::const_eval_raw_provider 30: rustc::ty::query::__query_compute::const_eval_raw 31: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query 32: rustc_mir::const_eval::eval_queries::const_eval_validated_provider 33: rustc::ty::query::__query_compute::const_eval_validated 34: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query 35: rustc_mir::const_eval::eval_queries::const_eval_validated_provider 36: rustc::ty::query::__query_compute::const_eval_validated 37: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::const_eval_validated>::compute 38: rustc::dep_graph::graph::DepGraph::with_task_impl 39: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query 40: rustc::mir::interpret::queries::<impl rustc::ty::context::TyCtxt>::const_eval_instance 41: rustc::mir::interpret::queries::<impl rustc::ty::context::TyCtxt>::const_eval_resolve 42: <rustc::traits::project::AssocTypeNormalizer as rustc::ty::fold::TypeFolder>::fold_const 43: rustc::ty::structural_impls::<impl rustc::ty::fold::TypeFoldable for &rustc::ty::TyS>::super_fold_with 44: <rustc::traits::project::AssocTypeNormalizer as rustc::ty::fold::TypeFolder>::fold_ty 45: rustc::traits::project::normalize 46: rustc_typeck::check::FnCtxt::normalize_associated_types_in 47: <core::iter::adapters::Map<I,F> as core::iter::traits::iterator::Iterator>::fold 48: rustc::ty::context::GlobalCtxt::enter_local 49: rustc_typeck::check::wfcheck::check_item_well_formed 50: rustc::ty::query::__query_compute::check_item_well_formed 51: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::check_item_well_formed>::compute 52: rustc::dep_graph::graph::DepGraph::with_task_impl 53: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query 54: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::ensure_query 55: __rust_maybe_catch_panic at src/libpanic_unwind/lib.rs:86 56: <std::panic::AssertUnwindSafe<F> as core::ops::function::FnOnce<()>>::call_once 57: __rust_maybe_catch_panic at src/libpanic_unwind/lib.rs:86 58: rustc_hir::hir::Crate::par_visit_all_item_likes 59: rustc_typeck::check_crate 60: rustc_interface::passes::analysis 61: rustc::ty::query::__query_compute::analysis 62: rustc::dep_graph::graph::DepGraph::with_task_impl 63: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query 64: rustc::ty::context::tls::enter_global 65: rustc_interface::interface::run_compiler_in_existing_thread_pool 66: scoped_tls::ScopedKey<T>::set 67: syntax::with_globals note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace. note: the compiler unexpectedly panicked. this is a bug. note: we would appreciate a bug report: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#bug-reports note: rustc 1.42.0-nightly (c2d141df5 2020-01-24) running on x86_64-unknown-linux-gnu note: compiler flags: -C opt-level=3 -C codegen-units=1 --crate-type lib note: some of the compiler flags provided by cargo are hidden query stack during panic: #0 [fn_sig] processing `Bug::a::{{constant}}#0::{{closure}}#0` #1 [is_const_fn_raw] checking if item is const fn: `Bug::a::{{constant}}#0::{{closure}}#0` #2 [const_eval_raw] const-evaluating `Bug::a::{{constant}}#0` #3 [const_eval_validated] const-evaluating + checking `Bug::a::{{constant}}#0` #4 [const_eval_validated] const-evaluating + checking `Bug::a::{{constant}}#0` #5 [check_item_well_formed] processing `Bug` #6 [analysis] running analysis passes on this crate end of query stack error: aborting due to 2 previous errors For more information about this error, try `rustc --explain E0015`. error: could not compile `playground`. To learn more, run the command again with --verbose. ``` </details>